560 Isolation of an “early” transit amplifying keratinocyte population in interfollicular human epidermis: a role for CD271 receptor

Abstract

In the interfollicular epidermis stem cells (KSC) generate transit amplifying (TA) cells that, after symmetric divisions, produce differentiating daughters. We isolated and characterized the highly proliferative interfollicular epidermal basal cell population “early” TA (ETA) cells, based on its capacity to adhere to type IV collagen. Proliferation and colony forming efficiency in ETA cells are lower than in KSC, but higher than in “late” TA (LTA). Stem and differentiation markers confirmed that ETA cell display a unique phenotype. Skin reconstructs derived from ETA cells present different features (epidermal thickness, Ki67 and survivin expression), as compared to skin equivalents generated from either KSC or LTA cells. The low affinity neurotrophin receptor CD271, that regulates the KSC to TA cells transition in human epidermis through an on/off switch control mechanism, is predominantly expressed in ETA cells. Skin equivalents generated from siRNA CD271 ETA cells display a more proliferative and less differentiated phenotype, as compared to mock-derived reconstructs. Consistently, CD271 overexpression in LTA cells generates a more proliferative skin equivalent than mock LTA cells. Finally, CD271 expression declines with ageing and cellular senescence. In addition, CD271 overexpressing cells show lower p16ink4a levels than mock cells during replicative senescence and CD271 also appears to delay senescence in ETA in comparison to LTA cells. We conclude that ETA cells represent the first KSC progenitor with exclusive features. CD271 identifies and modulates ETA cells, thus participating in the early differentiation and regenerative capacity of human epidermis.